is this to small for a six month old crested

i have a crested gecko who is around six months old and around 3 and a half inches long and hes missing his tail

At 6 months old I'd be more concerned about a cage being too big. Since you didn't mention what size cage you have, I can't comment on how appropriate it is.

size is gonna depend on what the crested was fed, temps, how often it was fed. a pic would be better and a weight

i have him in a 15 gallon tank and he is 10.2 grams

Just fine for a while :D

I keep my adults (30 grams+) in 20 gallon high aquariums, turned on end for more height.